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Full text of "On the Total Solar Eclipse of July 29th, 1878"

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1878.] 10d [Frazer. 

These represent in the rock — 

p. c. of (Si0 4 ) combined in ortho-silicates 22.67 

p. c. of (Si0 3 ) combined in mono-meta-silicates 28.12 



Total 50. 79 

It is interesting to note in conclusion that the rational formula calcu- 
lated for labradorite according to the modern chemical system and which 
regards this mineral as one of the para-silicates is 

(Ca li Al 2 vi ) viii (Si 3 iv O 10 u ) viii . 
This might be viewed as a mixed ortho- and mono-meta-silicate* in which 
there are two molecules of the radical (Si0 4 ) and one of (SiO H ). In the 
latter one of the atoms of O is employed in saturating alone, and the pro- 
portion which this bears to the total amount of oxygen in both radicals is 
evidently 1 : 11. 

In Pyroxene all the silica is present as mono-meta silicic acid. 

In a mixture containing exactly one molecule each of Labradorite and 
Pyroxene, there would then be : 

Orthosilicic Mono-meta- 



Acid. 



silicic Acid . 



Labradorite 2 1 

Pyroxene 1 

2 

That is, the number of molecules of Ortho- and Mono meta-silicic acid 
would be equal, or if the p. c. by weight of the latter were as above sup- 
posed, 22.67 in the rock, that of the latter would be in such a mixture, 
27.17 p. c. which is very nearly that actually given. 



On the Total Solar Eclipse of July 29th, 1878. 
By George F. Barker. 
(Bead before the American Philosophical Society, Nov. 15M, 1878.) 

The purpose of the present paper is to put on record in the Proceedings 
of the Society some account of the observations made by certain of its 
members upon the total solar eclipse of the 29th of July, 1878. 

The expedition was organized in June, by Professor Henry Draper of 
New York, out of compliment to whom, his associates named it the 
Draper Eclipse Expedition. The party consisted of Dr. Draper as Direc- 
tor, with Mrs. Draper as assistant, who were in charge of the photographic 
and photospectroscopic work, as also of the observations with the slitless 
spectroscope ; of President Morton, of Hoboken, to whom was confided 
the general observations, as well as those with the polariscope and pocket 
spectroscope ; of Dr. Thomas A. Edison, of Menlo Park, who was to 
use his newly invented tasimeter. in order to determine whether it was 

*See " Tables for the determination of minerals," Frazer. 1874. 



Barker.l W4: j- Nov# i5) 

possible to measure the heat of the corona; and of myself, who was to ob- 
serve with the analyzing spectroscope with the especial object of ascer- 
taining the presence either of bright or of dark (Fraunhofer) lines in the 
spectrum of the corona. 

Rawlins, Wyoming Territory, had been selected by the Director as the 
observing station, because while it was near the central line of totality, it 
was also easily accessible, being on the Union Pacific Railroad, was a place 
of some size, having eight or nine hundred inhabitants, and was the loca- 
tion of the railroad repair shops of the Laramie division, so that in case of 
need, assistance in constructing or repairing our instruments could be had. 
Moreover, it had a bountiful supply of excellent water brought in pipes 
from the neighboring Cherokee mountain, which being of granite, yielded 
a pure product of inestimable value for purposes of photography. Pre- 
vious experience in that region of country too, had assured Dr. Draper 
that the air there was dry, and hence that the chances of clear weather on 
the day of the eclipse were very considerable. 

The expedition left New York on the evening of the 13th of July ; and, 
resting by the way at Chicago for a day, reached Rawlins at mid-night of 
the 18th. The apparatus and material, which had been sent on by ex- 
press in advance, had already arrived and in apparently good order, 
though in all it weighed nearly a ton, After a day's reconnoitering, plans 
were perfected and arrangements made for the construction of a temporary 
observatory in which to shelter the larger instruments. An excellent site 
was selected by Dr. Draper, protected in great measure from the strong 
winds from the west which at times sweep over those mountain plains. 
In this building the telespectroscopes were erected, a portion of it being 
converted into a photographic dark room, and supplied with running 
water from the hydrant. The location of this observatory was determined 
to be latitude 41° 48' 50" K, longitude 2 h. m. 44 s. W. from Washing- 
ton. Its altitude above the sea level was 6,732 feet. The tasimeter tele- 
scope of Dr. Edison was erected in an adjoining building, facing the west 
and about ten or fifteen feet distant. 

The ten days of time which had been allowed for completing the pre- 
parations was found to be none too much. During a large portion of every 
day and most of the night, some or all of the party were engaged in ad- 
justment of the instruments, in practice with them, in determining posi- 
tions in photographic work, or in the numberless details necessary to 
success. On the night of the 24th, we were joined by the English astro- 
nomer, J. Norman Lockyer, F. R. S., and also by Professor James C. 
Watson, of the University of Michigan. Mr. Lockyer's work being mostly 
photographic, he was efficiently aided by Mr. J. B. Silvis, the owner of a 
photographic car traveling over the Union Pacific Railroad, which chanced 
at that time to be in Rawlins. Mr. Silvis not only most generously placed 
himself and his car at Mr. Lockyer's disposal for any experimental pur- 
poses -entirely free of expense, but on the day of the eclipse, he allowed 
him to take the car to Separation, about thirteen miles distant, assisted 
him in observing, and returned with him to Rawlins the same evening. 



1878.J 



105 



[Barker. 



The day of the eclipse was all that could be desired. The sky was 
almost without a cloud throughout, and the dew point was found to be at 
least 34° F. below the temperature of the air. The entire programme of 
observations was carried out as it had been arranged, and with singularly 
good fortune. "The results obtained," as summarized by Dr. Draper, 
" were : 1st, the spectrum of the corona was photographed and shown to be 
of the same character as that of the sun and not due to a special incan- 
descent gas ; 2d, a fine photograph of the corona was obtained., extending 
in some parts to a height of more than twenty minutes of arc, that is, of 
more than 500,000 miles ; 3d, the Fraunhofer dark lines were observed by 
both Professors Barker and Morton in the corona ; 4th, the polarization 
was shown by Professor Morton to be such as would answer to reflected 
solar light ; and 5th, Mr. Edison found that the heat of the corona was 
sufficient to send the index beam of light entirely off the scale of the gal- 
vanometer." As these results seem to be of very considerable importance, 
it appears desirable to give the various methods of observation somewhat 
more in detail, adopting for the purpose so far as possible the language of 
the observers themselves, as given in their several reports. 

Photographic and Phototelespectroscopic Observations. 



The instruments which were used 
by Dr. Draper in his photographic 
and phototelespectroscopic obser- 
vations were : " 1st. An equatorial 
mounting, with spring governor 
driving clock, loaned by Professor 
Pickering, Director of Harvard Ob- 
servatory. 2d. A telescope of five 
and a quarter inches aperture and 
seventy-eight inches focal length, 
furnished with a lens specially cor- 
rected for photography, by Alvan 
Clark & Sons. 3d. A quadruple 
achromatic objective of six inches 
aperture and twenty-one inches 
focal length, loaned by Messrs. E. & 
H. T. Anthony, of New York ; to 
this lens was attached a Rutherford 
diffraction grating nearly two inches 
square, ruled on speculum metal. 
This arrangement (Fig. 1.) with its 
plate holders, etc., will be desig- 
nated as a phototelespectroscope. 
Besides these there was a grating 
spectroscope, an eye slit! ess prism 

PROC. AMER. PHTLOS. SOC. XVIII. 102, N. PRINTED JAN. 25, 1879. 




Barker.] 106 [Nov. 15, 

spectroscope, with two inch telescope, and finally a full set of chemicals 
for Anthony's lightning collodion process, which in my experience is fully 
three times quicker than any other process." 

"The arrangement of the phototelespectroscope requires farther descrip- 
tion, for success in the work it was intended to clo, viz., photographing 
the diffraction spectrum of the corona, was difficult and in the opinion of 
many of my friends impossible. In order to have every chance of success 
it is necessary to procure a lens of large aperture and the shortest attain- 
able focal length, and to have a grating of the largest size adjusted in such 
a way as to utilize the beam of light to the best advantage. Moreover, the 
apparatus must be mounted equatorially and driven by clockwork so that 
the exposure may last the whole time of totality and the photographic 
work must be done by the most sensitive wet process. After some experi- 
ments during the summer of 1877 and the spring of 1878, the following 
form was adopted. 

"The lens being of six inches aperture and twenty-one inches focal 
length, gave an image of the sun less than one-quarter of an inch in dia- 
meter and of extreme brilliancy. Before the beam of light from the lens 
reached a focus it was intercepted by the Rutherford grating set at an angle 
of sixty degrees. This threw the beam on one side and produced there 
three images— a central one of the sun and on either side of it a spectrum ; 
these were received on three separate sensitive plates. One of these 
spectra was dispersed twice as much as the other, that is, gave a photo- 
graph twice as long. This last photograph was actually about two inches 
long in the actinic region. If, now, the light of the corona was from in- 
candescent gas giving bright lines which lay in the actinic region of the 
spectrum, I should have procured ring-shaped images, one ring for each 
bright line. On the other hand, if the light of the corona arose from in- 
candescent solid or liquid bodies, or was reflected light from the sun I was 
certain to obtain a long band in my photograph answering to the actinic 
region of the spectrum. If the light was partly from gas and partly from 
reflected sunlight a result partly of rings and partly a band would have 
appeared. 

"Immediately after the totality was over and on developing the photo- 
graphs, I found that the spectrum photographs were continuous bands 
without the least trace of a ring. I was not surprised at this result, be- 
cause during the totality I had the opportunity of studying the corona 
through a telescope arranged substantially in the same way as the photo- 
telespectroscope and saw no sign of a ring. 

"The plain photograph of the corona taken with my large equatorial on 
this occasion shows that the corona is not arranged centrally with regard 
to the sun. The great mass of the matter lies in the plane of the ecliptic 
but not equally distributed. To the eye it extended about a degree and a 
half from the sun toward the west, while it was scarcely a degree in length 
toward the east. The mass of meteors, if such be the construction of the 
corona, is therefore probably arranged in elliptical form round the sun. 

"The general conclusion that follows from these results is that on 



1878.] 



107 



[Barker. 



this occasion we have ascertained the true nature of the corona, viz: it 
shines hy light reflected from the sun hy a cloud of meteors surrounding 
that luminary, and that on former occasions it has been infiltrated with 
materials thrown up from the chromosphere, notably with the 1474 matter 
and hydrogen. As the chromosphere is now quiescent this infiltration has 
taken place to a scarcely perceptible degree recently. This explanation of 
the nature of the corona reconciles itself so well with many facts that have 
been difficult to explain, such as the low pressure at the surface of the sun, 
that it gains thereby additional strength. ' ' 

Tasimetric Observations. 
As this eclipse is the first in which any attempt has been made to measure 
the heat of the solar corona, Dr. Edison's report to Dr. Draper on this sub- 
ject is here quoted in full. He says : 

" The instrument which I used at Rawlins, Wyoming, during the solar 
eclipse of July 29th, 1878, for the purpose of measuring the heat of the 
sun's corona, was devised by me a short time only before that event, and 
the time was insufficient to give it as thorough a test as was desirable to 
ascertain its full capabilities and characteristics. 

"This instrument I have named the tasimeter, from the Greek words, 
tolgk;, extension, and fierpov, measure, because primarily the effect is to 
measure extension of any kind. The form of instrument which I used is 
shown in the annexed wood cut (Fig. 2.) 

Fig. 2. 




"With this instrument was used a Thomson's reflecting galvanometer 
on a tripod, having a resistance of three -fourths of an ohm. The galvanom- 
eter was placed in the bridge wire of a Wheatstone balance, two of the 
branches of which had constant resistances of ten ohms each, while of the 



Barker.] 



108 



[Nov. 15, 



other two one had a constant of three ohms, and the other contained the 
tasimeter which was adjusted by means of the screw to three ohms. When 
thus balanced, if the strip of vulcanized rubber A (seen in Fig. 3), placed 
between the fixed point B and the carbon button C, was exposed to heat 
from any source, it expanded, placing pressure upon the carbon button, 
decreasing in this way its resistance and destroying the balance ; thus allow- 
ing a current to pass through the bridge wire containing the galvanometer, 
the amount of this current of course being proportional to the expansion of 
the rubber and to the strength of the battery. 

"The form of instrument here described was finished only two days 
before leaving for the west ; hence, I was unable to test it. However, I 
set it up upon my arrival at Rawlins, but found that it was a very difficult 
matter to balance so delicate an instrument as a reflecting galvanometer 
with one cell of battery, through such small resistances. In fact, I did not 
succeed in balancing it at all in the usual way. Nor could it be balanced 
in any way until I devised a method which I may designate * fractional 
balancing/ when it became very easy to accomplish the result and also to 
increase the eftect by using two cells in place of a single one. This device 

Fig. 8. 




consisted of a rheostat formed of two rows of pins. The rows were about 
one-half an inch apart. A wire was connected from a pin on one row to a 
pin on the other row and so on, so that the current had to pass through 
the whole length of the wire, which was No. 24 gauge and four feet long. 
This was used as a shunt around the galvanometer. A copper wire con- 
necting all the pins of one row served to reduce the resistance to zero. 
When the galvanometer was thus shunted, a very feeble current passed 
through it. If the spot of light was not at zero it was brought there by 
either increasing or decreasing the pressure upon the vulcanite of the tasi- 
meter by the adjusting nut. When thus brought to zero the copper wire 
of the shunt rheostat was taken off of one pin, thus increasing the resist- 



1878.] 10J [Barker- 

ance of the shunt perhaps to one-fiftieth of an ohm. The spot of light was 
generally deflected nearly off of the scale. The light was again brought 
to zero by varying the resistance of the tasimeter, and another one-half 
inch of wire included in the shunt, another deflection and another balance 
was obtained by the tasimeter. Thus by gradually increasing the delicacy 
of the galvanometer by increasing the resistance of the shunt and balancing 
at every increase, the whole of the current was allowed to pass through 
the galvanometer and the shunt taken off. When this point was reached 
the damping magnet or director was in close proximity to the case of the 
galvanometer. To increase its delicacy to the fullest extent it became 
necessary to raise the director to the top of the rod. This was done by 
raising it cautiously a quarter of an inch at a time, bringing the spot of 
light to zero each time by the tasimeter. 

"In order to form some idea of the delicacy of the apparatus when thus 
adjusted, a preliminary experiment was made on the evening of the 27th, 
with the star Arcturus. The tasimeter being attached to the telescope, the 
image of the star was brought on the vulcanized rubber. The spot of 
light from the galvanometer moved to the side of heat. After some minor 
adjustments, five uniform and successive deflections were obtained with 
the instrument, as the light of the star was allowed to fall on the vulcanite 
to produce the deflection, or was screened off to allow of a return to zero. 

"It was in this condition when the eclipse occurred. The tasimeter 
was placed in a double tin case, with water at the temperature of the air 
between the walls. This case was secured to a Dollond telescope of four 
inches aperture. No eye piece was used. At the moment of totality the 
spot of light was slowly passing towards cold. When I withdrew a tin 
screen and allowed the edge of the luminous corona to fall upon the rubber, 
the spot of light stopped, went gradually off of the scale towards heat, its 
velocity accelerating as it approached the end. The time required for the 
light to leave the scale was from four to five seconds. 

"I interposed the screen and endeavored to bring the light back to zero, 
but I was unsuccessful. Had I known that the heat was so great I should 
have used a platinum strip in place of the vulcanite, and decreased the deli- 
cacy of the galvanometer by the approach of the damping magnet. 

"I would then doubtless have succeeded in getting two or more read- 
ings, and afterwards by comparison with bodies of known temperature 
would have obtained a near approach to the temperature of the sun's 
corona. ' ' 

Telespeotkoscopic Observations. 

My own results, obtained with an analyzing spectroscope attached to the 
telescope, seem to be almost unique in this eclipse. This fact must be my 
apology, if any be needed, for introducing here at such length, the facts of 
the case as contained in my report. 

The instruments and apparatus used in the observations were loaned for 
the purpose from the physical cabinet of the University of Pennsylvania. 
They consisted (1) of an equatorially mounted achromatic telescope of 
four inches aperture made by Jones of London ; (2) a direct vision astronom- 



Barker.] HO [Nov. 15, 

ical spectroscope by Merz of Munich; (3) a second direct vision spectro- 
scope by Hoffmann of Paris ; and (4) a pocket spectroscope by Geo. Wale & 
Co. Beside this spectroscopic outfit, a second four-inch achromatic tele- 
scope by Dollond was taken for use with the tasimeter by Dr. Edison, and 
a Savart, a Senarmont, and an Arago polariscope, for determining the 
polarization of the corona. The Merz spectroscope above mentioned is 
described in the "Philosophical Magazine," IV., xli., Feb., 1871. It is 
provided with two compound direct vision prisms, of which one or both can 
be used at pleasure, each consisting of five single prisms, two of flint glass 
with a refracting angle of 84°, and three of crown ; one of these having a 
refracting angle of 84°, the others of 87°. The dispersive power of each 
of these compound prisms is about equal to that of two equilateral prisms 
of flint glass. The instrument has a collimating and an observing tele- 
scope, each furnished with an object glass two-thirds of an inch in aper- 
ture and four inches in focal length. The prism-tube is attached to the 
collimator by two centres, giving it a lateral motion about a line passing 
through these centres, which constitutes an axis parallel to the slit. The 
observing telescope is similarly attached to the tube carrying the prism. 
These motions serve to alter the incidence of the rays upon the surface of 
the prism, and also to bring any special part of the spectrum into the mid- 
dle of the field. The observing telescope is provided with a positive eye- 
piece of an equivalent focal length of one inch, and also with a needle 
micrometer, having an eye-piece of one-half inch focus. The graduations 
upon this micrometer are strongly cut, enabling the positions and the dis- 
tances of the lines measured with it to be easily read even in a faint light. 
The spectroscope was firmly attached to the draw tube of the equatorial 
telescope by means of an open frame made by Zentmayer, so that the posi- 
tion of the image with reference to the slit could be readily observed. 

The time from the date of our arrival at Riwlins until the eclipse, was 
occupied in setting up the instruments, in getting them into adjustment, 
and in practice with them. It was found that with only one of the com- 
pound prisms of the Merz spectroscope, the slit being placed radially, it 
was easy to observe the lines C and F reversed in the chromosphere, and 
also the bright line D. { . On the morning of the day of the eclipse, the 
solar edge was examined for protuberances, in order to locate them in ad- 
vance of totality. But a single one was noticed, this being on the south- 
western edge of the sun. As the time of first contact approached, the 
spectroscope was removed and a paper screen was attached to the draw- 
tube, an image of the sun being formed on this screen by means of the 
eye-piece ; thus enabling the time of this contact to be approximately de- 
termined and the subsequent progress of the eclipse to be conveniently 
observed. No spots were seen under these circumstances, though this 
could hardly have been expected since the solar image was so small, 
scarcely three inches in diameter, unless the spots were of large size. As 
the time of second contact drew near, the spectroscope w T as replaced upon 
the equatorial. Since you deemed it of importance to pay special attention 
to the oxygen lines in the vicinity of G, the micrometer of this instrument 



1878.] HI [Barker. 

was, at your suggestion, so adjusted that one of its needle-points rested on 
the hydrogen line nearG and the other on the line known as h. After the 
last ray of sunlight had disappeared, I took a few seconds of the precious 
time to observe the eclipse with the naked eye. The moon appeared in- 
tensely black, surrounded by a pinkish halo, extending to about two fifths 
of a lunar diameter from the limb, and occupying the entire circumfer- 
ence. At two points this halo was expanded ,into radial streamers, one of 
which had parallel sides with a deeply indented or swallow-tailed end, ex- 
tending westward of the sun and apparently lying in the ecliptic ; the other 
appeared single, was on the eastern edge, and was inclined twenty degrees 
or more to the north of the ecliptic. The former of these streamers was 
traced to a distance of about a lunar diameter and a half from the edge, the 
latter to a somewhat less distance. No structure could be seen in the halo, 
but in the streamers traces of parallel rays appeared to be present. The 
amount of light emitted by the corona was a surprise to me. Preparations 
had been made for using artificial light for reading the circles, but this was 
found not to be at all necessary. The amount of light seemed to be nearly or 
quite equal to that given by the moon when ten days old . No protuberances 
were seen with the naked eye ; nor were any streamers observed, other 
than those already described. A glance at the eclipsed sun was then taken 
through the finder of the equatorial. The magnifying power being low, 
the corona presented much the same appearance as to the naked eye ; but 
the streamers showed much more distinct evidences of a radiated structure 
and a pale rosy protuberance was observed on the south-western edge of 
the dark disk. This was undoubtedly the same prominence which was 
observed previous to totality. 

Turning my attention now to the spectroscope, upon the slit of which 
the coronal image had already been brought by means of the finder, the 
slit being placed radially, the first glance through the instrument showed 
me a bright, but an absolutely continuous spectrum. The region under 
examination w T as of course that portion of the spectrum which had been 
placed before totality between the needle-points of the micrometer. Totally 
unprepared for so unexpected a result, I moved the observing telescope so 
as to bring the green portion of the spectrum into the field, expecting cer- 
tainly to see 1474 K, and by the appearance of this line to determine whether 
my instrument was out of adjustment ; and if it were, to adjust it again. 
But no bright line was there ; the green region appeared as continuous as 
the blue. I then gradually closed the slit — which had been previously ad- 
justed on the solar spectrum so that the line D appeared nebulous on its 
edges — thinking that I might in this way improve the definition, but with 
no better results ; no bright lines could be seen. To my great surprise, 
however, when the slit was thus narrowed, the region which was then 
under examination, that extending from b to G, appeared filled with dark 
lines on the brighter background, these dark lints being readily recognized 
from their general appearance as the solar lines of Fraunhofer. Still intent 
on getting bright lines, I opened the slit again gradually, moved the observ- 
ing telescope over the entire length of the spectrum from red to violet, re- 



Barker.] llZ [Nov. 15, 

peating tlie operation three times and varying the width of the slit from 
time to time in each region ; but not a single bright line could be detected. 
I then requested you to come and take a glance through my spectroscope, 
as had been previously agreed ; saying that although I could see dark lines 
and a continuous spectrum, I was unable to detect a single bright line, and 
knew not what to make of it. You were then looking at the eclipse through 
your ingenious little telespectroscope of two inches aperture. You came 
to my instrument, looked at the spectrum, moved the observing telescope 
over its whole length and remarked that the results in my spectroscope 
agreed entirely with those in yours, and that in both the spectrum appeared 
continuous, showing no bright lines whatever. 

My mind being thus relieved, I took my place again at the spectroscope, 
and this time, placing the slit tangential to the moon's limb, I moved the 
observing telescope from end to end of the spectrum, opening and closing 
the slit at intervals ; but the spectrum appeared as continuous as before. 
Again the image was adjusted so that the slit was once more radial; and 
this time on a still different portion of the corona. On examining again 
the spectrum, no bright lines appeared, except once for an instant, when 
the slit passed over the small chromospheric prominence already noticed. 
Warned by Mrs, Draper's clear and distinct counting that the precious 165 
seconds had two-thirds gone, I decided to devote the time still remaining 
to a more careful observation of the dark Fraunhofer lines. Now, for the 
first time, as I adjusted the width of the slit and its position on the corona 
with more care, I observed that these lines did not pass clear across the 
field, but were of a length corresponding to the width of the coronal 
image on the slit. At the base of the spectrum, which corresponded to 
the base of the corona, they appeared bright and sharp ; certainly quite as 
much so as in the light of the moon similarly condensed ; though the con- 
tinuous spectrum which formed their background was relatively brighter 
than in moonlight. There w T as no difficulty in identifying them as Fraunhofer 
lines from their general appearance and position ; but some of them could 
be identified beyond question. Such were b and F, which were especially 
distinct, D, E and G, which were considerably less so. They faded gradu- 
ally out from the base of the spectrum upward, appearing to end where 
the continuous spectrum of the corona was limited above. While thus 
employed, a flash of sunlight told us that totality had ended and that the 
solar eclipse of 1878 was over. 

In discussing the results of the spectroscopic observations which have 
now been detailed, I am, in the first, place, quite at a loss to account for the 
fact that no bright lines were seen by ine, notwithstanding the persistent 
efforts made to get them. The failure to observe them can be accounted 
for, as it would seem, only on the ground that with the dispersive power 
employed, the bright lines w&re too faint to be seen on the much brighter 
background of the continuous spectrum. 

The lessons to be drawn from these spectroscopic observations appear to 
be few and simple. The absence of bright lines, or at least of any which 



1878] H*> [Barker. 

were at all brilliant, proves clearly the absence in the solar coronal region 
of any considerable mass of incandescent gas or vapor ; which shining by 
its own light would of course give a bright line spectrum. The presence 
of Fraunhofer lines in the coronal spectrum shows conclusively the pres- 
ence of reflected sunlight, in the light of the corona and goes to establish 
the theory long ago suggested, that masses of meteoric matter raining 
clown upon the solar surface from all directions, reflected to us the light of 
the sun and were therefore the essential cause of the coronal phenomena. 
And, finally, the fact of the increased brightness of the continuous spec- 
trum, as compared with the intensity of the dark lines of Fraunhofer, goes 
to strengthen the probability that there is still other light in the corona 
which comes to us from the incandescent liquid or solid matter of these 
incandescent meteoric masses. These conclusions, deduced very simply 
from my own spectroscopic results, agree completely, I am happy to find, 
with those drawn from your most excellent photographs, as well as from 
the ingenious heat-measurements of Dr. Edison and the polariscopic deter- 
minations of Dr. Morton. 

General Conclusion. 

The general conclusion then, arrived at by the observations of our party 
upon this eclipse — a conclusion to which all the results point with singu- 
lar unanimity— is that the solar corona consists of a mass of meteoric 
bodies falling in from space upon the solar surface, which meteors 
being intensely heated by the resistance encountered at their enor- 
mous velocity, as well as by radiation from the sun, become highly 
luminous, and emit a light which gives a continuous spectrum. More- 
over, this mass of incandescent meteors is shown not to be equally 
extended in all directions around the sun, but appears to be ellip- 
soidal or at least spheroidal in form. That the larger part of the coronal 
light comes from the incandescence of these meteors, there can apparently, 
be but little doubt. But a considerable portion of it appears to have quite 
a distinct origin, and to be due to the reflection of solar light by these solid 
or liquid masses. Hence the appearance of the dark solar or Fraunhofer 
lines in the spectrum. A third, and in this eclipse an extremely small 
portion of the light of the corona, would seem to be due to incandescent 
gaseous matter, either injected into it from below, or produced from the 
meteoric masses themselves by the intense heat. This portion it is which 
gives the bright line spectrum, as feeble in this eclipse as it was strong in 
previous ones. Of the material composing this gas, there is yet, as it would 
appear, no indication. 

From what has now been narrated, it must be conceded that the Draper 
Eclipse Expedition was singularly and exceptionally fortunate. No small 
part of this good fortune is due, as we believe, to the courtesy and liberality 
of the railroad and express companies over whose routes either the party 
or their instruments traveled. I desire to mention especially, in this con- 
nection, Col. Thos. A. Scott and Mr. Frank Thomson, of the Pennsylvania 

PKOC. AMER. PHILOS. SOC. XVIII. 102. O. PRINTED JAN. 21, 1879. 



Barker.] 114 [Nov 15, 

Railroad ; Mr. Henry Keep and Mr. M. L. Sykes, of the Chicago and North- 
western Railroad ; Mr. Sidney Dillon and Mr. Jay Gould, of the Union 
Pacific Railroad ; Mr. William H. Fargo, of the American Express Com- 
pany ; Mr. Frederic Lovejoy, of Adams' Express Company, and the Super- 
intendent of the Union Pacific Express Company. The cordial appre- 
ciation by these gentlemen of the fact that the work in which we were en- 
gaged was one of a purely scientific character, and as such was one to which 
every reasonable facility should be furnished, was as gratifying to us as it 
was honorable to them. I should fail to do exact justice were I to omit 
mention of the service rendered us by Mr. J. J. Dickey, the Superintendent 
of the Union Pacific Telegraph; Mr. E. Dickenson, Superintendent of the 
Laramie Division; Mr. R. M. Galbraith, Superintendent of the Repair Shops 
at Rawlins ; Major Thornburgh, Commanding Officer at Fort Fred Steele, 
with Capt. Bisbee and Surgeon De Witt, his associates in the service ; 
Mr. Lawrence Hayes, of the Railroad Hotel, and to Mr. J. B. Silvis, of 
the photographic car. " Of the citizens of Rawlins, " says Dr. Draper, " it 
is only necessary to say that we never even put the lock on the door of the 
observatory, and not a thing was disturbed or misplaced during our ten 
days of residence, though we had many visitors." 

The agreeable party, the pleasant surroundings, the charming weather, 
the kindness of friends, and above all, the capital success of the observa- 
tions, make the Draper Eclipse Expedition an exceedingly pleasant 
memory to us all. 



Notes on a series of Analyses of the Bolomitic Limestone Bocks of Cumber- 
land County, Pa., made by Messrs. Hartsliorne and Hartranft in the 
Laboratory of the Second Geological Survey of Pennsylvania. By J. P. 
Lesley, State Geologist. 

(Bead before the American Philosophical Society, October 18th, 1878.) 

At a meeting of the American Philosophical Society, Dec. 20, 1877, I 
described the progress of an elaborate investigation which I had instituted 
for the purpose of determining whether or not any fixed or rational order 
of deposition could be observed in our Lower Silurian, or Siluro- Cambrian 
Magnesian Formation (No. II). 

I selected a fine exposure made by the rock cut of the Northern Central 
Railroad, on the west bank of the Susquehanna river, opposite Harrisburg, 
where a consecutive series of the beds, all conformable and all dipping 
regularly about 30° to the southward, afforded a good opportunity for col- 
lecting two sets of specimens for analysis, one at the bottom and the other 
at the top of the cut ; and great care was taken to survey the cut, mark the 
beds (from 1 to 115) and range the specimens in two parallel series ; so